The present invention relates to optical signal detector, and relates more particularly to a dual-beam detector for an electro-optical mouse.
A variety of functional control devices are known and widely used in controlling a display cursor. These devices have taken several forms. They can be gathered into two categories basically: a mechanical type, or an optical type. A mechanical cursor control device is generally comprised of a ball controlled to move on a work pad. An output indicative of the direction and amount of movement of the cursor control device is produced and employed to move the cursor on a display screen. This structure of mechanical cursor control device is not very reliable, particularly over long periods of use. An optical cursor control device, or an electro-optical mouse, is generally comprised of a lens used to magnify the images taken on a work pad relative to the direction and amount of movement of the cursor control device, permitting the magnified images to be reflected onto a receiver by a reflector, which receiver converts the images into electronic signals indicative of the direction of movement of the cursor control device, for moving the cursor from position to position on a display screen. In order to differentiate the images for the X-axis from the images for the Y-axis, the work pad may be made in two colors so that a special photo sensor can detect X-axis signals from Y-axis signals. However, this arrangement greatly increases the cost of the cursor control device. There is an alternate method used to detect X-axis signals from Y-axis signal. This alternate method is to assign the top edge of the work pad for the X direction and the bottom edge thereof for the Y-direction. This arrangement increases the total thickness of the work pad and reduces the reliability of tracking.
In order to eliminate the aforesaid disadvantages, there is provided an electro-optical cursor control device which utilizes a cylindrical lens to magnify images longitudinally. This arrangement improves the reliability. However, the optical cursor control device should be kept in course while tacking on a work pad. Any minor deviation may affect the reliability of the cursor control device. As illustrated in FIGS. 8 and 9, distortion occurred to the magnified lines that were imaged while the cursor control device biased from course.